1. FIELD OF THE INVENTION
This invention relates to a method of removal of slag deposits from the bottom of a furnace. The invention is especially advantageous when applied to the soaking pits in which steel ingots are heated for rolling into slabs, but in principle is applicable to other furnaces employed in the iron and steel industry. The invention will be described here mainly in relation to soaking pits.
2. DESCRIPTION OF THE PRIOR ART
Scale formed on the ingots falls off in the soaking pit and forms slag deposits on the bottom of the pit. The deposits build up with continued use of the pit so that the bottom surface of the pit rises. This brings the ingots closer to the flames at the top of the pit, so that the rate of scale formation increases.
It is known to try to remove loose deposits by means of a mechanical grab, but most deposits become sintered and cannot be removed in this manner. It is the current practice to take the pit out of operation, when the bottom surface rises too high, and to loosen the slag with pneumatic drills to enable its removal. This is a highly unsatisfactory procedure. It is expensive in labor. The pit must be allowed to cool for six days and, in order to avoid damage by thermal expansion, must be reheated slowly over ten days. There is thus a considerable need for a removal process which does not require cooling down of the furnace. No successful process of this kind has hitherto been developed.
The prior art contains various proposals. U.S. Pat. No. 4,165,065 describes, with particular reference to open hearth and electric furnaces, a process of adding a melting point lowering substance (especially alumina) to a still hot build-up of lime and then applying further heat to liquefy the combined material so that it can be drained away. Likewise U.S. Pat. No. 4,018,622 proposes removal of dusts, slag etc. in copper smelting furnaces by means of special fluxes which form a flowable glass. U.S. Pat. No. 3,365,523 describes the addition of fluxing material to the combustion chamber of a burner directed against slag in a furnace; presumably the furnace is generally cooled previously. DE NO. 711297 (1940) is concerned with the removal of iron oxide slags from pusher furnaces for rolling mills, by adding a mixture of solid fuel and oxygen-providing material to produce liquefaction.